The present invention relates to electronic devices, and, more particularly, to semiconductor devices useful in communications.
Communications aboard an airplane for pilot control of wing flaps, tail flaps, engine power, and so forth were originally by cables running from the cockpit to the various controlled devices. Reliability and complexity of control communications led to the substitution of hydraulic systems for the cable systems, and then the substitution of electrical systems for hydraulic systems. Such electrical systems are constrained by requirements of high reliability and small available space. Multiple backups and noise tolerance help reliability, and balanced differential signals provide maximal noise immunity. Early electrical systems such as ARINC-429 use direct point-to-point wiring. Later systems such as MIL-1553 use a multiplexed serial data bus with Manchester coding to save weight by sharing a common bus cable. The still more recent ARINC-629 standard uses magnetic coupling into a bus cable without piercing the insulation of the cable; this gives higher reliability at the expense of more complex coding. Thus airplane control communication systems need efficient conversion between the usual Manchester encoded serial information and ARINC-629 protocol serial information.
Problems of conversion between Manchester and ARINC-629 signals include the generation of pairs of pulses (for the ARINC-629 doublets) of stable duration, with minimal delay between the input and the pulse pair output, and without the use of a crystal oscillator or system clock due to time delays or space limitations. Also, to increase reliability, the differential receivers need fault detection capability. This includes both the checking of an incoming signal for proper waveshape and the self-diagnosis of faults in he receiver circuitry.
Abidi, 22 IEEE J.Sol.St.Cir. 494 (1987) describes a switched capacitor feedback loop to linearize a voltage controlled oscillator. Wakayama and Abidi, 1987 IEEE Int.Sol.St.Cir.Conf. 220 (1987) describe a voltage controlled oscillator with a frequency to voltage servo loop to linearize the oscillator.
Liu and Meyer, 1988 IEEE Int.Sol.St.Cir.Conf. 22 (1988) use a frequency to voltage converter to linearize a voltage controlled oscillator and include a master slave arrangement to calibrate the oscillator frequency by locking to a crystal reference frequency.
Ware et al, 24 IEEE J.Sol.St.Cir. 1560 (1989) describe a reference voltage and a reference current generated from the same bandgap circuit so the references track and errors cancel.
The present invention provides pulse pair generation with stabilized pulse widths plus abutting opposite polarity portions without reliance on crystal oscillators or clock synchronization plus also provides fault detection within the paired transmission wiring.